Description of the Prior Art
Pumps, that is to say apparatus for displacing fluids, which are at present available have some disadvantages. In particular, the apparatus can become blocked, particularly when solid material is to be pumped, and some blockages can require dismantling of the apparatus to enable the blockage to be cleared. Also, particularly when solids are being pumped, crushing of the solids can occur which is undesirable.
Also it is desirable that the pumping rate of the apparatus for displacing fluids be variable and it is desirable that the same torque be delivered per stroke regardless of the pumping rate.